Production of electrical switch contact elements



Much 13, 1956 F. ROLLFINKE 2,737,708

PRODUCTION OF ELECTRICAL SWITCH CONTACT ELEMENTS Filed Dec. 12, 1951 2z--[ 4: I l

IN V EN TOR. Palace/.4 0 F/NAE' BY MMgM United, States Patent PRODUCTION OF ELECTRICAL SWITCH CONTACT ELEMENTS Friedrich Rolliinke, Reutte, Tirol, Austria, assignor to Schwarzkopf Development Corporation, New York, N. Y., a corporation of Maryland Application December 12, 1951,, Serial No. 26, 1,574

2 Claims. (Cl. 29--155.55)

This invention relates to the production ofelectrical switch contact elements and more particularly, to the production of thin andfiat contact elements out of refractory metals such as tungsten, molybdenum and their alloys.

Among the objects of the invention is a more effective way for producing generally flat contact elements of 2,737,708 I Patented: Mar. 1 3", 1 95 8 wire se'ctio'ns' required'for the contact elements, either by-a shear or by a cutting disk. When a'shear is used for cutting the thintungsten wire into the short wire sections, the loss of the refractory wire material ispracticallyzero. When a cutting disk is used for cuttingth'e thin tungsten wire into the short wire sections, the loss in the refractory'wiremetal is only small since the length of each wire section is a multiple of the thickness of the cutting disk in contrast with the prior art production method wherein the cutting disk has a thickness substan tiall'y equal to the thicknessof the contact element.

Because: of the large applied deformation to which they are subjected in their-production by the process of the invention, the resulting thin tungstencontact elements have not onlya fine grain structure and high ductility, but in addition, they exhibit in operation very desirable recrystallization characteristics. These desirable structural properties give such switch contact elements of theinvention the great advantage of operating" with surprisingly small contact arcing or burningloss and they have accordingly an unusually long operating life.

Without thereby in any way li'm-itingthe scope of-the invention, but in orderto enable ready practice thereof, there are given below, by way of example, data of'a practical applicationthereof. l

A tungsten wire of circular cross-section having a diameter of two millimeters was cut into longitudinal 'wire sections, each 9 millimeters long. Eachlongitudinal wire section was then compressed by compression jaws en- Disk-like thin switch contact elements of tungsten or? other refractory metals, such as tungsten and molybdenum alloys, have found a wide field of application, particularly as contact elements for ignition circuit switches of internal combustion engines. In most cases, such thin flat contact elements are formed out of a tungsten rod, having a diameter or cross-sectional area equal to the area of the desired flat contact element, by cutting the relatively thick tungsten rod with a cutting disk into the desired thin contact elements. 'Since the cutting disk has a certain minimum thickness, a substantial part in most cases about one-halfof the tungsten rod is ground off into tungsten dust-as the tungsten rod is cut by the cutting disk into the contact elements, and a substantial volume of tungsten is thus lost. I

Among the objects of the invention is the production of thin flat switch contact elements of the foregoing type which avoids the loss of the valuable refractory metal heretofore incurred incident to the production of such contact elements. According to the invention, the desired switch contact elements are produced by first providing a refractory metal wire having a diameter or cross-sectional area materially smaller than the area of the desired switch contact elements and after cutting the wire into a' plurality of short wire sections" thereafter compressing the' individual wire sections in their axial direction into thin and relatively wide fiat contact elements of the desired contact surface area. A tungsten wire having a diameter about half the diameter of the desired contact element disk is suitable for producing in an effective way contact elements in accordance with the process of the invention.

The individual wire sections may be heated to an elevated temperature of about 1000 C. and higher when compressed into larger diameter thin contact elements of the invention.

Thus, in the case of tungsten contact elements, good results are obtained by using a tungsten wire having a diameter about half the diameter of the desired contact element and then axially compressing short sections of such tungsten wire into contacts having a diameter twice the wire diameter. i

The thin refractory metal wire may be cut into the short gaging the opposite ends of each wire section. The wire is heated while being compressed, either by passing'cur rent therethrough or by externally applied heat. When heated by passing electric current through each compressed wire section, the compression jaws may be used as electrically conductive terminal connections to the wire ends.

The accompanying drawing shows diagrammatically, essential elements of a mechanism used in forming contacts in accordance with the principles of the invention. The mechanism comprises an upper press member '11 and a lower press member 12 of a conventional press which are arranged to be moved towards each other for compressing between them a small object with the required large force. carry along their facing surfaces two pressing inserts 13 and 14 of electrically conducting hard material, such as ,tungsten or metal carbide of a cross sectional area greater thickness. In practice, tungsten contact elements of the type shown are principally used as distributor switch contacts for .ignition distributors of automotive vehicles and like applications. In such applications, the individual tungsten contacts are about lmillimeter thick and about 4 to 6 millimeters wide.

In the pressing operation, current is passed from one of the pressing inserts 13 through the thin wire section 21 to the other pressing insert 14 for heating the tungsten wire section to an elevated temperaturebetween about 700 and 1000 C. at which the tungsten Iwire section loses the brittleness which it has at room temperature and acquires substantial ductility, and the two insert members 13,14 are brought against each other by the pressing members 11, 12 to compress the heated tungsten wire sections 21 to the shape of the disc-like contact element 22. The cross-sectional area of the thin wire section 21 is only a fraction of the area of the two pressing inserts 13, 14 between which it is compressed, so that the heating The two opposite press members 11, 12

current shall bring the thin wire section 21 to the required high temperature without changing the temperature of the pressing inserts 13, 14.

It has been found that when heating the compressed tungsten wire sections by passing heating current therethrough, good results are obtained by using compression jaws of tungsten for also passing heating current through the compressed wire sections. Tungsten has good hotstrength and also good electrical and heat conductivity, and by forming the current supplying compression jaws of tungsten there is avoided excessive heating of the compression jaws compressing the heated tungsten wire sections into relatively large diameter thin contact elements. Good results are obtained by heating the tungsten wire sections to a temperature of about 1300 C. while or before they are compressed by the compression jaws into the large-diameter thin contact elements.

The features and principles underlying the invention described above in connection with specific exemplifications, will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims be construed broadly and that they shall not be limited to the specific details shown and described in connection with exemplifications thereof.

I claim:

1. In the process of forming relatively flat and thin disk-like contact elements consisting essentially of tungsten, the procedure comprising the steps of providing a wire of said refractory metal having a cross sectional area which is at most about one half the surface area of the fiat contact element to be formed, subdividing said wire in a direction transverse to the axis of said wire into elongated wire sections of the volume of the contact element to be formed, heating the said individual wire sections to an elevated temperature at which the tungsten of said wire section loses its brittleness and acquires a high degree of ductility and compressing the said individual thin wire sections in an axial direction whereby said section is radially expanded to form said disk-like contact elements having relatively large extended areas of a width materially greater than their thickness.

2. The process as claimed in claim 1, the heating of the individual wire sections and compressing of said wire sections in said axial direction being effected by applying to the opposite ends of each individual wire section two opposite jaws of refractory metal, supplying current from opposite poles of an electric energy source to said opposite jaws and therethrough to the opposite ends of each wire section placed between said jaws and thereby heating each wire section by current flowing by way of said opposite jaws through said wire section and bringing the temperature of each wire section to said elevated temperature and also moving at least one of said jaws towards the other in the axial direction of said wire section until the heated wire section is flattened into a disc-like contact element having extended opposite surface areas at least twice the cross-sectional area of said wire section.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE PROCESS OF FORMING RELATIVELY FLAT AND THIN DISK-LIKE CONTACT ELEMENTS CONSISTING ESSENTIALLY OF TUNGSTEN, THE PROCEDURE COMPRISING THE STEPS OF PROVIDING A WIRE OF SAID REFRACTORY METAL HAVING A CROSS SECTIONAL AREA WHICH IS AT MOST ABOUT ONE HALF THE SURFACE AREA OF THE FLAT CONTACT ELEMENT TO BE FORMED, SUBDIVIDING SAID WIRE IN A DIRECTION TRANSVERSE TO THE AXIS OF SAID WIRE INTO ELONGATED WIRE SECTIONS OF THE VOLUME OF THE CONTACT ELEMENT TO BE FORMED, HEATING THE SAID INDIVIDUAL WIRE SECTIONS TO AN ELEVATED TEMPERATURE AT WHICH THE TUNGSTEN OF SAID WIRE SECTION LOSES ITS BRITTLENESS AND ACQUIRES A HIGH DEGREE OF DUCTILITY AND COMPRESSING THE SAID INDIVIDUAL THIN WIRE SECTIONS IN AN AXIAL DIRECTION WHEREBY SAID SECTION IS RADIALLY EXPANDED TO FORM SAID DISK-LIKE CONTACT ELEMENTS HAVING RELATIVELY LARGE EXTENDED AREAS OF A WIDTH MATERIALLY GREATER THAN THEIR THICKNESS. 